Centrifugal blower with external overdrive

ABSTRACT

A centrifugal gas compressor is disclosed that includes an external drive mechanism consisting of a plurality of pulleys arranged to provide an overdrive in rotational speed. The pulleys are connected with belts to provide a reliable, efficient, cost effective, and readily scalable means of power transmission between the associated motor and the compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

BACKGROUND

[0002] 1. Field of Invention

[0003] This invention is a centrifugal blower with an improved drivemechanism that includes an external overdrive pulley.

[0004] 2. Description of Prior Art

[0005] Centrifugal blowers, also known as superchargers, have been usedin a number of applications since their introduction in the 19^(th)century to move air in forging operations. Centrifugal blowers have anumber of applications, including industrial air movers, and powerenhancements for internal combustion engine. In addition, they have beenused in automotive applications, airplane wing de-icers, snow blowers,food handlers, electronic component dryers, inflation devices, and evenmilitary weapons. A centrifugal blower consists of

[0006] (1) a spinning impeller that pulls air in from the center andforces it out radially

[0007] (2) a scroll that guides the air from the center of the impellerto the discharge near the edge

[0008] (3) a drive mechanism to rotate the impeller

[0009] (4) associated hardware to couple the major components

[0010] To increase the output for a given size and configurationsupercharger, the impeller is often turned faster than the drive motor.This is typically accomplished by an “overdrive” unit built into thesupercharger. The exact overdrive ratio is up to the designer, but inputto output speed ratios of 3:1 to 10:1 are common. The input shaft of theoverdrive unit is typically turned by a belt system.

[0011] The overdrive can be accomplished in a number of ways. One of theearly commercial superchargers by McCulloch and Paxton used a planetarydrive system. In this system, an input shaft rotates an array of fingersthat in turn rotate a number of balls pressed against an impeller shaft.The rotation of the balls rotates the impeller shaft and, hence, theimpeller. A more recent example of friction-type drive was described byShirai in U.S. Pat. No. 5,158,427. This design used roller pins insteadof balls to achieve a comparable overdrive. The amount of overdrivebetween the input and impeller shafts is dictated by the dimensions ofthe components. The key to these systems is the high friction betweenall of the components to prevent slippage. Unfortunately, a system withhigh internal friction requires significant additional input power toovercome the frictional losses. The frictional loss increases internaltemperatures at the expense of efficiency and reliability.

[0012] More recent designs have used gears to achieve the overdrive.See, for example, the U.S. Pat. No. 5,224,459 to Middlebrook (1993).While the gear system results in slightly increased reliability and issimpler to produce, it still has some major drawbacks. The first is thatgears make noise, particularly when spinning at the speeds of 30,000 to50,000 RPM typically run by blowers. It is well known that the noise ofa gear system can be reduced by using helical-cut gears instead ofstraight-cut ones, but helical-cut gears develop an axial thrust thatmust be absorbed by the bearings causing additional heat generation andwear. Another disadvantage of gear systems is the requirement of anoiling system. This adds to both the cost and complexity ofinstallation. In the case of automotive superchargers, the oiling systemfor the gears is often plumbed into the engine's system. This creates anadditional risk where debris from the supercharger, e.g., from gearwear, can enter the engine's oiling system and reduce engine life.

[0013] Another method of driving the impeller is through the use ofsprockets and cog belts. The U.S. Pat. No. 5,887,576 to Wheeler (1999)describes one such form of an internal overdrive for superchargers. Inthis patent, the internal drive mechanism comprises input and outputshafts with sprockets that are connected by a cog belt. By making thesprocket on the input shaft larger in diameter than the one on theoutput shaft, the speed of the output shaft is increased. Theinput-to-output ratio is similar to that employed with gear overdrives.In theory, the cog belt provides an efficient overdrive mechanism.However, designs such as the one described in the Wheeler patent have anumber of shortcomings, many of which are related to the sizeconstraints on the internal drive system. In practice, the spaceavailable for the internal overdrive mechanism is about the same size,or more precisely the same diameter, as the supercharger. This dictatesthat the pulleys are small and the belt is very short. Small pulleysincrease the duty on the belt by forcing it to bend around a tighterradius. Short belts increase the number of belt revolutions per pulleyrevolution and further increase the duty on the belt. The net result ofboth of these factors is a severely reduced belt life. Air vents toreduce belt temperature, such as those described in U.S. Pat. No.5,887,576, could theoretically improve the situation, but experience hasshown the belt life to be unacceptably short.

SUMMARY

[0014] In accordance with the present invention, the supercharger has anexternal overdrive system comprised of pulleys of optimized sizerotationally coupled by an appropriate number of belts in conjunctionwith a number of other inherent supercharger components and hardware.

[0015] Objects and Advantages

[0016] Accordingly, besides the objects and advantages of superchargers,as described above, several objects and advantages of the presentinvention are:

[0017] (a) to reduce the size of the supercharger and increaseflexibility of design and installation;

[0018] (b) to reduce the noise level of the drive mechanism;

[0019] (c) to reduce the operational duty on the belt and increase beltlife;

[0020] (d) to reduce operational temperatures of the belt and increasebelt life;

[0021] (e) to improve the overall supercharger reliability; and

[0022] (f) to simplify the design of a supercharger and reducemanufacturing costs.

[0023] Further objects and advantages will become apparent from aconsideration of the ensuing description and drawings.

DRAWING FIGURES

[0024]FIG. 1 shows a cut-away view of the supercharger, including thecompact bearing case, and the external drive mechanism.

[0025]FIG. 2 shows a front view of the supercharger and overdrive pulleysystem attached to a simple drive pulley.

[0026]FIG. 3 represents one possible arrangement of the invention in asingle accessory belt automotive application.

[0027] Reference Numerals in Drawings 10 impeller 12 scroll 14 diffuserplate 16 bearing case 17 bearing case bolt 18 main bearing 20 main seal22 main shaft 24 input pulley 26 supercharger bracket 30 input belt 32output overdrive pulley 34 input overdrive pulley 36 overdrive bearing38 overdrive pulley shaft 39 overdrive pulley bracket 40 drive belt 42drive pulley 50 accessory belt 52 accessory pulley 54 idler pulley 56tensioner pulley 58 air conditioning pulley 60 alternator pulley 62power steering pulley 64 water pump pulley

DESCRIPTION

[0028]FIG. 1—Preferred Embodiment

[0029] A preferred embodiment of the invention is shown in FIGS. 1 and2. The invention consists of a bearing case 16 and a direct connectionfrom an input pulley 24 to an impeller 10 by means of a main shaft 22positioned by two main bearings 18. Main seals 20 are located adjacentto the main bearings 18 to protect them from dust and debris. Theimpeller 10 rotates inside of a scroll 12. As the impeller 10 rotates,it draws air from the inlet at the center of the scroll 12. Thecentrifugal energy imparted by the rotating impeller 10 pushes the airto the outer diameter of the scroll 12, compresses it, and forces it outthe scroll 12 discharge.

[0030] In centrifugal blower designs, the quantity of gas displaced bythe unit is a function of, among other variables, rotational speed ofthe impeller 10. Typically, the desired speed of the impeller 10 ishigher than the speed of the rotating equipment available to drive it.For this reason, a overdrive of some type is required. The disclosedinvention utilizes an external overdrive, as depicted in FIGS. 1 and 2.The overdrive arrangement includes an input overdrive pulley 34rotationally coupled to an output overdrive pulley 32. The two pulleysare free to rotate about an overdrive pulley shaft 38 and overdrivebearings 36 supported by an overdrive pulley bracket 39. The inputoverdrive pulley 34 is coupled to a drive pulley 42 associated with aninternal combustion engine by a drive belt 40 capable of transferringthe rotational force from the drive pulley 42 to the input overdrivepulley 34. By specifying the diameter of the input overdrive pulley 34to be smaller than the diameter of the drive pulley 42, the inputoverdrive pulley 34 will undergo a greater number of revolutions forevery drive pulley 42 revolution. The ratio of the rotational speeds isgiven by the ratio of pulley diameters. The output overdrive pulley 32,being fixed at the center of the input overdrive pulley 34, rotates withthe same number of revolutions per unit time. The output overdrivepulley 32 is coupled to the input pulley 24 by means of an input belt 30capable of transferring the rotational force from the output overdrivepulley 32 to the input pulley 24. The input belt 30 is of the multipleribbed design to increase grip. Since the diameter of the outputoverdrive pulley 32 is larger than the diameter of the input pulley 24,the input pulley 24 undergoes a greater number of revolutions per unittime than the output overdrive pulley 32. The ratio of the rotationalspeeds is again given by the ratio of pulley diameters. The net resultis that the input pulley 24 can be rotated at a greater speed than thedrive pulley 42 associated with the internal combustion engine.

[0031] Additional Embodiment

[0032] One additional embodiment of the invention is its application asan industrial blower. In this case, the invention could be used tocompress and transport any industrial gas, including air, in the samemanner described in the preferred embodiment. The only practicaldifference would be that the drive pulley 42 could be coupled to anelectric motor or a suitable internal combustion engine.

[0033] Alternative Embodiments

[0034] There are a number of arrangements possible with the currentinvention. Without wishing to limit the broad and versatile nature ofthe invention, some representative examples are listed below:

[0035] (a) cogged belts can be used in combination with, or as areplacement for, standard v-belts or multiple ribbed belts;

[0036] (b) two or more overdrive pulley sets can be used to achieve ahigher ultimate rotational speed or to reduce the ratio of eachoverdrive;

[0037] (c) the belts and pulleys of the invention could be enclosed witha separate cover, while maintaining the advantages of an external drivesystem.

[0038] Advantages

[0039] From the description and drawings above, a number of advantagesof the invention become evident:

[0040] (a) The compact size of the supercharger nose piece, or bearingcase, provides additional freedom in the design and installation. Thisis particularly valuable when the available space for a supercharger islimited, as is often the case in automotive applications.

[0041] (b) By utilizing an external overdrive system, the heat generatedby the system is not transferred to the supercharger itself andparticularly the bearings and seals.

[0042] (c) By using a belt and pulley arrangement rather than gears toachieve the overdrive, the noise generated by the unit can bepractically eliminated.

[0043] (d) The external overdrive arrangement allows larger diameterpulleys and greater pulley-to-pulley spacing to be used. Both of thesehave the effect of increasing belt life.

[0044] (e) In the event that there is a failure of a component of theexternal overdrive, the component can be repaired or replaced withoutdisassembling the supercharger.

[0045] (f) The external overdrive arrangement also allows greaterfreedom in the design with regard to size and placement of components.This allows a number of off-the-shelf components to be used which cangreatly reduce manufacturing cost.

[0046] Operation—FIG. 3

[0047] The applications of the current invention are very similar to theapplications of other supercharger systems in present use. An example ofan automotive application is depicted in FIG. 3. The accessory pulley 52of an automobile rotates an accessory belt 50 that drives the rest ofthe engine's accessories, including the air conditioner pulley 58, thealternator pulley 60, the power steering pulley 62 and the water pumppulley 64. Idler pulleys 54 and a tensioner pulley 56 are used to ensureproper power transmission. In this example, the accessory belt 50 isalso used to turn the input overdrive pulley 34 that, in turn, rotatesthe supercharger. The exact types, numbers, and placement of belts andpulleys is determined by the specific design. The same principles applyfor both automotive and industrial applications of superchargers.

[0048] Conclusion, Ramifications and Scope

[0049] Accordingly, the reader will see that the supercharger describedin this invention has a number of advantages over the prior art in termsof performance, reliability, simplicity, cost of manufacture andflexibility of design.

[0050] Although the description above contains many specificities, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of the presently preferredembodiments of this invention. For example, sealed bearings could beused to eliminate the need for separate seals and bearings. Also, thevolume of the bearing case could be of any size and could thus be usedas a reservoir for any oil required by the bearings. On the overdrivepulley shaft, the bearings could just as easily be placed in theoverdrive pulley bracket with the pulleys pressed onto the shaft. Thusthe scope of the invention should be determined by the appended claimsand their legal equivalents, rather than by the examples given.

I claim:
 1. A centrifugal compressor system with an external rotationaloverdrive mechanism comprising: (a) a scroll with an inlet to receivethe gas to be compressed and an outlet to discharge the compressed gas;(b) a diffuser plate secured to the rear of said scroll and enclosingsaid scroll to form a sealed chamber; (c) a bearing case housing two ormore bearings with seals and attached to said diffuser plate; (d) ashaft that is supported by said bearings, passing through said bearingcase, said diffuser plate and at least partway through said scroll; (e)an impeller rotatably attached to said shaft and contained in the sealedchamber between said scroll and said diffuser plate; (f) an input pulleyrotatably attached to the opposite end of the said shaft from saidimpeller capable of rotating said shaft and impeller; (g) a centrifugalcompressor bracket with a plurality of holes as a means for locatingsaid diffuser plate; (h) an external overdrive system comprising: aninput overdrive pulley; an output overdrive pulley rotationally coupledto said input overdrive pulley and rotatably supported on an overdriveshaft with one or more sealed bearings; an overdrive pulley bracket witha plurality of holes as a means for locating said input and outputoverdrive pulleys a fixed distance from said input pulley such that saidoutput overdrive pulley rotates in the same plane as said input pulley;(i) an input belt attached to said output overdrive pulley and saidinput pulley capable of rotating said input pulley while said inputoverdrive pulley is rotated; and (j) a drive belt attached to andcapable of rotating said input overdrive pulley and means rotating saiddrive belt.
 2. The centrifugal compressor system of claim 1 where thetension in either or both of said input and drive belts is maintained bymovement of said external overdrive system relative to said inputpulley;
 3. The centrifugal compressor system of claim 1 with a rotatablymounted idler pulley engaging said input belt to maintain the desiredlevel of tension in said input belt.
 4. The centrifugal compressorsystem of claim 1 with a rotatably mounted idler pulley engaging saiddrive belt to maintain the desired level of tension in said drive belt.5. The centrifugal compressor system of claim 1 wherein said drive beltis rotationally coupled to a drive pulley on an internal combustionengine for use as a supercharger.
 6. The centrifugal compressor systemof claim 1 wherein said drive belt is rotationally coupled to a drivepulley on an internal combustion engine or an electric motor for use asan industrial blower.
 7. The centrifugal compressor system of claim 1wherein said input belt, said input pulley and said output overdrivepulley are a multiple ribbed design.
 8. The centrifugal compressorsystem of claim 1 wherein said drive belt, said drive pulley and saidinput overdrive pulley are a multiple ribbed design.
 9. The centrifugalcompressor system of claim 1 wherein said input belt, said input pulleyand said output overdrive pulley are a cogged design.
 10. Thecentrifugal compressor system of claim 1 wherein said drive belt, saiddrive pulley and said input overdrive pulley are a cogged design.